Sintering Operations In Powder Metallurgy
In powder metallurgy, the hardest thing is obtaining uniform density from the produced product. And the flow of the metal powder through the mold sections is another problem. Isostatic pressing processes are developed because of these reasons.
Here we explain the general working principle, advantages, and disadvantages of the isostatic pressing processes. Also, you can find information about the two types of isostatic pressing processes.
The isostatic pressing process is the alternative compaction of the metal powders inside special molds to obtain more uniform densities and more complex geometries with a better flow of the metal.
Isostatic pressing is applied with flexible lateral molds, which are shaped with the application of lateral hydraulic pressures. With the application of pressurized fluid from the lateral sections of a rubber mold. Rubber mold will take the required shape with the pressure and the same pressure will compact the metal powder.
There are two types of isostatic pressing processes; cold isostatic pressing(CIP) and hot isostatic pressing(HIP).
As you understand from the name, the isostatic pressing is applied at room temperature. And the fluids to apply hydrostatic pressure are water or oil. Molds of the cold isostatic pressing process are made from elastomer materials. Molds are designed oversized to compensate for the shrinkage.
The most important advantage of the cold isostatic pressing is the cheap tooling. And because of this, cold isostatic pressing processes are more suitable for low production.
The Uniform density of the obtained product is another important aspect of the cold isostatic pressing process.
Dimensional accuracy is the biggest problem for the cold isostatic pressing processes. Because of the flexible molds, tolerances are problematic issues. So, additional machining or other processes must be applied to parts that are produced with the cold isostatic pressing.
The application principle of the hot isostatic pressing process is nearly the same as the cold isostatic pressing process. But the main difference is that the hydrostatic pressures are obtained with high-temperature gases such as helium or argon.
Molds of the hot isostatic pressing are made from sheet metals to withstand high temperatures.
The most important advantage of the hot isostatic pressing process is the both compacting and sintering operations are done in one step, because of the application of pressure.
But the main disadvantage of the hot isostatic pressing process is the expensive tooling. Because of this, these processes are applied only to special applications such as aerospace applications.
The produced parts with the hot isostatic pressing process are generally good in mechanical strength because of the low porosity.
The general aspects of the isostatic pressing processes can be explained like that.
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